How to Use DPDT 5v Relay: Examples, Pinouts, and Specs

The Double Pole Double Throw (DPDT) 5V relay is an electromechanical switch that allows you to control two independent circuits simultaneously. Operating at a 5V DC input, this relay can switch between two states, enabling both on/off control and direction switching. It is widely used in applications requiring electrical isolation, such as motor control, home automation, and industrial systems.

• Motor direction control (e.g., forward/reverse)
• Switching between two power sources
• Home automation systems
• Signal routing in audio or communication systems
• Industrial control systems

Below are the key technical details of the DPDT 5V relay:

The DPDT relay typically has 8 pins. Below is the pinout description:

1. Power the Relay Coil: Connect the coil pins (1 and 2) to a 5V DC power source. Use a transistor or relay driver circuit to control the coil, as the relay may require more current than a microcontroller pin can supply.
2. Connect the Load:
   • For the first circuit, connect the load to COM1 (pin 3) and either NC1 (pin 4) or NO1 (pin 5), depending on the desired default state.
   • For the second circuit, connect the load to COM2 (pin 6) and either NC2 (pin 7) or NO2 (pin 8).
3. Control the Relay: Use a microcontroller, switch, or other control signal to energize the relay coil. When the coil is energized, the relay switches from NC to NO for both poles.

• Back-EMF Protection: Always use a flyback diode across the coil terminals to protect your circuit from voltage spikes when the relay is de-energized.
• Current Ratings: Ensure the load current does not exceed the relay's maximum switching current (10A).
• Isolation: The relay provides electrical isolation between the control circuit and the load, making it safe for high-voltage applications.

Below is an example of how to control a DPDT 5V relay using an Arduino UNO:

// Define the pin connected to the relay control circuit
const int relayPin = 7; // Connect this pin to the base of a transistor or relay module

void setup() {
  pinMode(relayPin, OUTPUT); // Set the relay pin as an output
  digitalWrite(relayPin, LOW); // Ensure the relay is off initially
}

void loop() {
  // Turn the relay on
  digitalWrite(relayPin, HIGH); 
  delay(5000); // Keep the relay on for 5 seconds

  // Turn the relay off
  digitalWrite(relayPin, LOW); 
  delay(5000); // Keep the relay off for 5 seconds
}

Note: Use a transistor (e.g., 2N2222) or a relay driver module to interface the Arduino with the relay, as the Arduino pin cannot directly supply the required current.

1. Relay Not Switching:

   • Cause: Insufficient current to the coil.
   • Solution: Use a transistor or relay driver circuit to provide adequate current.

2. Chattering or Unstable Operation:

   • Cause: Noise or insufficient power supply.
   • Solution: Add a capacitor (e.g., 100µF) across the power supply to stabilize it.

3. Load Not Switching:

   • Cause: Incorrect wiring of the load to the relay terminals.
   • Solution: Double-check the connections to COM, NC, and NO pins.

4. Burnt Relay Contacts:

   • Cause: Exceeding the relay's current or voltage ratings.
   • Solution: Ensure the load does not exceed the relay's maximum ratings.

Q1: Can I use the DPDT 5V relay with an AC load?
A1: Yes, the relay can switch AC loads up to its rated voltage and current. Ensure proper isolation and safety precautions.

Q2: Why do I need a flyback diode?
A2: The flyback diode protects your circuit from voltage spikes generated when the relay coil is de-energized.

Q3: Can I control the relay directly with a microcontroller?
A3: No, most microcontroller pins cannot supply enough current to energize the relay coil. Use a transistor or relay driver module.

Q4: What is the difference between NC and NO terminals?
A4: NC (Normally Closed) is connected to the common terminal when the relay is inactive, while NO (Normally Open) is connected when the relay is active.